The Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) Screening Trial is a large randomized trial to determine if screening for these cancers reduces mortality. The Trial is carried out by the NCI under contract with investigators at ten clinical centers in the United States. The study includes approximately 155,000 volunteers (recruited from 1993 through 2001, ages 55-74, equally distributed to the screening and control arms of the Trial). The PLCO Etiology and Early Markers Study (EEMS) supports etiologic and early detection studies of cancers and other conditions. EEMS uses data and samples collected in the context of the PLCO Trial including:1. Baseline demographic and risk factor information on all participants,2. Food Frequency Questionnaires(FFQ) on all participants3. Fractionated blood specimens at each of six screening rounds from screened participants,4. Buccal cell samples from control participants, and5. Information on all-cancer incidence and selected other medical conditions.The PLCO EEMS is a national resource, actively managed by the NCI and directed towards meeting the Institute's strategic priorities in molecular epidemiology and early detection. Etiologic and early marker investigations are carried out in collaboration with Christine Berg, MD, Project Officer, PLCO Trial and Phil Prorok, PhD, Chief Statistician, PLCO Trial. The NCI maintains follow-up of cohort members and a PLCO EEMS research database and sample inventory, and initiates additional risk factor and biologic materials collection, including collection of pathologic material. In addition, in conjunction with research activities in PLCO EEMS, NCI investigators develop added-value resources, including validation of biochemical and cytogenetic markers, tissue arrays for pathologic samples (in planning), nutritional modules for FFQs, and assays for genetic analysis (http://snp500cancer.nci.nih.gov). NCI scientists, study center investigators and others use these resources to address important issues in clarifying the etiology of cancers and in the development of effective early markers of disease. Multi-investigator studies of determinants of colorectal tumors (Cas ID: 00040), prostate (Cas ID: 10003), breast, endometrial, lung, and pancreatic cancer are underway. Other investigations include determinants of tobacco use, risk factors for benign prostatic hyperplasia, and protein early detection markers for cancer.